Cardiac stimulation systems commonly include a pulse-generating device, such as a pacemaker or implantable cardioverter/defibrillator that is electrically connected to the heart by at least one medical electrical lead. A medical electrical lead delivers electrical pulses emitted by the pulse generator to the heart, stimulating the myocardial tissue via electrodes included on the lead. Cardiac signals may also be sensed by lead electrodes and conducted, via the lead, back to the device to monitor the electrical activity of the heart. These leads are coupled to the devices via connector terminals carrying one or more contact surfaces, which are in turn coupled to corresponding lead electrodes by elongate conductors extending within the lead.
In recent years, with the development of cardiac resynchronization therapy, pacing of the left ventricle has been achieved by implanting transvenous lead electrodes in the coronary venous system of the heart to stimulate an epicardial surface of the left ventricle. Precise placement of lead electrodes through the coronary veins is often difficult, forcing clinicians to work around sub-optimal pacing thresholds and/or unwanted extra-cardiac stimulation, for example phrenic nerve stimulation. Transvenous leads including a plurality of electrodes can provide an increased opportunity to provide more optimal pacing in that, once the lead is best positioned within a coronary vein, a choice of pacing sites is provided by the plurality of electrodes. Furthermore, pre-shaped distal portions of leads can enable stable placement of electrodes and enhance contact between the electrodes and electrically active cardiac muscle.